As President of the Senate he served as Acting Governor for three and a half days in January 2002 following the resignation of Governor Christine Todd Whitman. Bennett's predecessor as Senate President, Donald DiFrancesco had previously served as acting Governor, and Bennett in turn succeeded to the office of acting governor when DiFrancesco's term ended and he was elected as the new Senate President.

During his service as acting governor, Bennett appeared on national television as part of the "five governors in a week" news cycle. He signed legislation into law, appointed judges, granted a pardon, created a nursing advisory council, and hosted several parties at Drumthwacket. The nursing advisory council was a tribute to his wife, Peg, a nurse. Peg Bennett was active during her tenure as First Lady of New Jersey.

In June 2002, Bennett was involved in a shoving match with South JerseyDemocratic Party boss and Commerce National Insurance CEO George Norcross after Norcross threatened to publicize a pardon Bennett gave during his three day executive tenure if Bennett could not convince his fellow Republican senators to vote for a tax increase and stadium construction bill in committee.

Bennett fell out of favor as a result of allegations that he overbilled the municipality of Marlboro Township for legal services. In a statement to the press, Bennett blamed party bosses and a biased press for attempting to destroy him. Bennett was a leading opponent of using state funds to construct a convention center/stadium in Pennsauken Township, New Jersey that would have been used by a minor leagueice hockey team that Norcross had bought an interest in.

In the 2005 primary election he was elected Republican State Committeeman for Monmouth County. John O. Bennett is also a professor at Montclair State University. In June 2012 he was elected the chairman of the Monmouth County Republican Party Committee during its annual reorganization meeting.[2]

^Mansnerus, Laura. "Jersey State House Loses Race and Party's Hopes", The New York Times, November 5, 2003. Accessed November 26, 2007. "Mr. Bennett, a moderate Republican who became the highest-ranking Republican officeholder in the state amid Democratic gains in the Senate and General Assembly two years ago, conceded defeat at around 9:30 p.m. following a rough race against Ellen Karcher, Marlboro township's council president, who took 52 percent of the vote. Mr. Bennett got 43 percent, and the Green Party candidate, Earl Gray, received 5 percent."